1. Field of the Invention
The invention generally relates to high performance bipolar pedestal transistors and, more particularly, to a method for making such transistors in which the intrinsic collector junction is very narrow and in which the extrinsic collector junction is substantially eliminated.
2. Description of the Prior Art
High performance bipolar transistors are known in which switching speed is greatly improved by the elimination of the extrinsic base-collector junction and the undesired capacitance associated with it. In the absence of base-collector capacitance domination, speed-power characteristics at lower power can be further improved by the reduction of the extrinsic base resistance. Such resistance reduction has been achieved by the provision of a low resistance, contiguous polycrystalline silicon base contacting member.
The foregoing techniques are disclosed in U.S. Pat. No. 3,796,613, issued to I. E. Magdo et al on Mar. 12, 1974, for "Method of Forming Dielectric Isolation For High Density Pedestal Semiconductor Devices" and assigned to the present assignee.
It is further advantageous that all of the foregoing considerations be accomplished in a manner permitting narrowing of the intrinsic collector junction so as to maximize device density in integrated chips. According to the technique disclosed in the aforementioned patent, silicon is deposited through an oxide layer which is apertured over the intrinsic collector region. Epitaxial growth results only in the exposed, recessed collector region, as desired, provided that the oxide window delineating said region is at least a certain size so that "bridging" can not occur. Although, ideally, no silicon should deposit on the raised oxide surrounding the collector region aperture, there remains a tendency to do so unless critical silicon deposition conditions are maintained reliably. Any undesired polycrystalline silicon deposits on the surrounding oxide tend to "bridge" over the aperture, preventing desired deposition within the aperture, especially where the aperture is made small for high component density.